The present invention generally relates to wireless communication. More specifically, the invention relates to a method and apparatus for scheduling of associated signaling information.
Recently, there has been a trend in the telecommunication community to focus more and more on wireless packet data communication rather than wireless circuit switched communication. With the tremendous increase of Internet users, and usage of Internet protocols, it is believed that the packet switched communication will soon become larger than the circuit switched communication that today dominates, e.g., the cellular communication. Cellular communication system manufacturers and operators are therefore looking for solutions to integrate their circuit switched services with wireless packet switched services that can provide reliable and more spectrum efficient connections for packet switched users, e.g., Internet users. This trend has made different types of packet switched communication system evolutions flourish. One of the more well known packet switched cellular systems in the telecommunications community, is the extension of the present GSM cellular communication system, called GPRS (General Packet Radio Service).
GPRS is a packet switched system that uses the same physical carrier structure as the present GSM cellular communication system and is designed to coexist and provide the same coverage as GSM. GPRS radio interface is thus based on a TDMA (Time Division Multiple Access) structured system with 200 kHz carriers divided into eight timeslots with GMSK (Gaussian Minimum Shift Keying) modulation. The multiplexing is such that multiple users can be allocated on the same timeslot, and resources are utilized only when data needs to be transmitted. A single user can also be allocated on multiple timeslots to increase the throughput of data over the air interface.
The GPRS specification includes a number of different coding schemes to be used dependent on the quality of the radio carrier. With GPRS, data rates well over 100 kbps will be possible.
There is also ongoing a development and standardization of a new air interface mode in GSM, which will affect both packet and circuit switched modes. This new air interface mode is called EDGE, Enhanced Data rates for Global Evolution. The main features of EDGE are new modulation and coding schemes for both packet switched and circuit switched data communication. In addition to the Gaussian Minimum Shift Keying (GMSK) modulation, which is used today for both GPRS and GSM circuit switched mode, an 8 symbol Phase Shift Keying (8PSK) modulation is introduced. This modulation can provide users with higher data rates than GMSK in good radio environments.
The packet data mode with EDGE modulation is called EGPRS (Enhanced GPRS) and the circuit switched data mode is called ECSD, (Enhanced Circuit Switched Data). With EGPRS and 8 PSK modulation, data rates over 384 kbps will be possible.
Recent developments for another TDMA based cellular system, the cellular communication system compliant to the ANSI/136 standard, referred to below as TDMA/136, has been focused on a packet data system to be integrated with the TDMA/136 circuit switched mode.
This packet data system will also be based on the new EDGE technology as defined for the GPRS extension. It will then allow TDMA/136 operators with a packet data mode to provide data rates up to 384 kbps on 200 kHz carriers with GMSK and 8PSK modulation as defined for EGPRS.
While the evolution of cellular packet data communication previously has been focused on developing a system that efficiently utilizes resources to transfer data which is non-delay sensitive (often referred to as best-effort data), the focus is now shifting towards the transmission of data for delay sensitive applications and higher quality of service requirements. The main application is voice communication.
While it is today rather straightforward to establish and maintain a circuit switched connection for delay sensitive voice communication, a packet switched connection is traditionally designed for non-delay sensitive applications, such as downloading of files, and not for voice communication. There are several things in a packet data system designed for “best-effort” data that require modifications to make it suitable for delay sensitive applications such as voice communication.
One important area still to be solved is the transmission of control signals in packet data transfer mode, i.e., when occupied in a data transfer on an allocated transmission resource.
In present EGPRS/GPRS networks, signaling of control signals while occupied in data transfer is typically handled by transmissions on a logical control channel called Packet Associated Control Channel (PACCH) that share transmission resources with the associated data stream. While this scheme works well for non-delay sensitive applications, it is not an advantageous method for delay sensitive applications. The signaling of control information requires allocation of transmission resources and if these are shared with the voice communication, there will be interrupts when control signaling is required. At present, there is no support for control signaling during packet data transfer mode in an GPRS/EGPRS system without interrupting the ongoing data flow. In circuit switched GSM, additional transmission resources are defined for a Slow Associated Control Channel, (SACCH), such that transmission of control information associated with a traffic channel (TCH) does not introduce interrupts in the ongoing traffic communication. The SACCH can be viewed as a “side stream” flow of information, both from the base station to the mobile station and in the opposite direction.
It would be advantageous also to introduce such an SACCH in a packet switched system, in order to transmit control information in a “side stream” in a bandwidth efficient way, thereby avoiding unwanted interrupts in, e.g., a voice communication over packet data.